The goals of this project are to accurately define the structural characterstics of the passive human knee. Our efforts to date have concentrated on the development of the experimental apparatus and on the experimental techniques. The current apparatus allows us to input desired displacements across the human knee joint, while measuring all of the associated forces and moments. The displacements are applied by an electrohydralic load frame, while the forces and moments are measured by specially designed force dynamometers capable of measuring all forces and moments at an accuracy of 1.5% of full scale. The data is digitized, stored, reduced and presented via special programs and a laboratory based computer. Studies on experimental techniques have shown that maintaining knee specimens at 21 degrees Centigrade, one hundred percent humidity, allows for maintaining mechanical characteristics over long periods of test time. Freezing at minus 25 degrees Centigrade, thawing and re-equilibrating in the storage system again produces the original mechanical characteristics. The cycling effects were observed to reduce the stiffness of the knee joint. However, storage in the above system will restore the original mechanical characteristics. The knee was also found to be rate dependent. However, a two order of magnitude change in rate from 20 seconds per cycle to 0.2 seconds per cycle resulted in only a 12% stiffening. During the next year we will be using the equipment and techniques to measure the contributions of approximately ten different identifiable soft structures to forces and moments across the joint. The motions will include: transverse displacements in the medio-lateral, anterior-posterior, and proximal-distal directions. Axial rotations and varus-valgus rotations will also be input at various centers of rotation. These data will characterize the stiffness characteristics of the human knee and the contributions of specific passive elements.